Data processing systems typically include volatile memory such as random access memory RAM which can be altered or written-into under control of the system controller or CPU. Often the information contained in the volatile memory is data which has been manually entered into the memory and should be protected from accidental destruction. Undesirably, however, noise and system malfunctions can cause erroneous write commands which result in incorrect data being written over valid data in the volatile memory. Thus, a problem exists to provide write-protection for volatile memory of data procesing systems.